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Arterial versus venous changes in vascular capacitance during nitroprusside infusion: a vascular modelling study
S Y Wang1, N W Scott-Douglas, D E Manyari
1Department of Medicine, The University of Calgary, AB, Canada.
Canadian Journal of Physiology and Pharmacology
|October 27, 1999
Summary
Nitroprusside (NP) increases vascular volume primarily through active changes in both arterial and venous capacitance. Despite similar magnitude increases, venous capacitance contributed more to the overall volume change due to its larger size.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
Background:
- The specific distribution of nitroprusside (NP)-induced changes in vascular capacitance between arterial and venous compartments remains unclear.
- Understanding these changes is crucial for comprehending NP's hemodynamic effects.
Purpose of the Study:
- To quantify and compare the effects of nitroprusside on canine ileal arterial versus venous capacitance.
- To determine the relative contributions of arterial and venous compartments to NP-induced increases in vascular volume.
Main Methods:
- Measurement of canine ileal arterial and venous pressures and total vascular volumes using scintigraphy before and during NP infusion.
- Application of a two-compartment model and literature data to estimate changes in venous and arterial capacitance.
- Manipulation of flow to restore perfusion pressure during NP infusion to assess dynamic volume changes.
Main Results:
- Nitroprusside infusion (decreasing perfusion pressure by 30%) increased total vascular volume to 111% of control.
- Restoring perfusion pressure by increasing flow further elevated vascular volume.
- Under constant flow, NP increased venous volume by 10.0% and arterial volume by 18.1%. When pressure was restored, venous volume increased by an additional 3.7% (arterial: 2.6%).
Conclusions:
- Nitroprusside induces vascular volume expansion primarily through active increases in both arterial and venous capacitance.
- Although arterial and venous capacitance changes were of similar magnitude, the larger baseline venous volume resulted in a greater absolute increase in venous volume.
- These findings elucidate the distribution of NP's vascular capacitance effects, highlighting the significant role of the venous system.